As usadka - very serious hindrance on a way to durability of a plaster covering, we will stop more in detail on the reasons, its generating.

Usadka depends on character tverdenija knitting and from quantity and structure of fillers. The matter is that the water entering into a solution, does not go entirely on chemical reaction. Its Any part simply fills emptiness between sand grains, and then evaporates, leaving in the hardened weight of emptiness.

If by the time of water evaporation knitting yet has not got sufficient durability the weight at the expense of the formed emptiness shrinks.

To Prevent it correct selection of fillers helps. It is important, that their grains as it is possible adjoined with each other, forming the original skeleton interfering usadke more densely. Then and medlennotverdejushchie solutions will not lose in volume.

It is not observed usadka in solutions with bystroshvatyvajushchimisja knitting (plaster, etc.). Tverdenie such solutions comes before full evaporation of water.

As at plaster works durability of a solution has even smaller value, than absence usadki small surplus of a filler is less dangerous, than surplus of the knitting.

We have started talking about sand - one of making any solutions - and we see that it makes essential impact on quality of plaster, as, naturally, and other components of a solution: fillers, additives, water. We Will dwell upon all these components and their influence on properties of building solutions.

First of all, we will continue conversation on sand.

On large rastvornyh knots there is a rule not simply to measure any sand in the necessary quantity, but also to know, sand possesses what properties. For this purpose define volume of emptiness in sand and krupnost its grains. For different layers of a solution grains of sand of the different size are necessary. For top (nakryvochnogo) a layer they should be 0,3... 1,2 mm, for the first layers of earth are supposed in the size to 2,5 mm.

For definition of emptiness take the big glass beaker (capacity 1,5, pour there 0,4 l. Then a thin stream pour strictly measured 1 l of sand. We will assume that the water level in a beaker has risen to a mark of 1,1 l. But we took 0,4 l of water and 1 l of sand, and have received in the sum not 1,4 l, and on 0,3 l it is less. This figure also will show us volume of emptiness in sand between its grains which was occupied with water.

Krupnost of grains define consecutive sifting of certain quantity of sand through a sieve with different krupnostju cells. Usually take a sieve with cells of 1,2 and 0,3 mm. Pass 2 kg of sand. If on the first sieve there was more than 1 kg of sand - it is considered large. If through a sieve with cells of 0,3 mm will pass over 1 kg sand is considered small. In other cases - an average on krupnosti.

For more exact definition of structure of sand on krupnosti grains use the whole set sit with krupnostju cells from 0,15 to 5 mm.

For durability of a solution it is better to use ostrorebristyj sand - mountain which rough surface provides good coupling with knitting, especially at limy solutions.

In plaster solutions ostrorebristogo sand it is necessary to consider application obligatory for limy solutions, supposing round, obkatannyj sand only for the cement.

The Best sand considers sand quartz.

Sand share on:

mountain - with angular grains;

ovrazhnyj - with even more angular grains;

river - with the rounded off grains;

sea - too with the rounded off grains, smaller, than in river.

Except a configuration of grains, sand differ also presence of impurity. Organic impurity, and clay negatively influence properties of a solution. At mountain sand always there are clay impurity. In ovrazhnom - the top layer is polluted, and more low where sand is washed out by ground waters, - pure. Sea sand contains salts and fossils. River - the purest. All it should be considered at drawing up rastvornoj weights, to check quality of sand. It not so is difficult. Take 3%-s' solution kausticheskoj soda and shake up in it the same quantity of sand. In a day colour of a liquid will show suitability of sand: if it only slightly yellowish - in it is not present organic impurity, it is suitable for a solution; yellow and dark-brown colours speak about unfitness of sand.

To Delete organic impurity it is difficult. Water them you will not wash up - it is necessary or prokalivanie, or washing by alkalis, and it is expensive.

With removal of clay business is easier: it is successfully washed away by water.

Already it was said above that on the taken filler distinguish heavy and easy solutions (them still name accordingly cold and warm).

Applied as a filler natural river or, more often, mountain sand possess the big density, from here and the big weight of a solution.

The Easy (warm) solution receive, using as a filler artificial slag or pumiceous sand - a porous material, and also some domain slags, asbestos and even fillers of an organic origin - a drevesno-coal trifle, sawdust, a fiber, a fire, etc.

Obligatory making a solution - water. First of all, it should be pure, drinking, not contain considerable mineral inclusions.

It is important to enter a certain quantity of water into a solution. You will take it more norms - the weight will be liquid, begins to flow down from walls, and, having dried up, plaster will appear insufficiently strong. At a lack of water the solution badly lays down on a surface and exfoliates.

It is good to work with a plastic solution, and its reception depends not only on use of the necessary quantity of water. So-called softeners help.